1. Field of the Invention
The present invention relates to a wire-sawing machine which can previously inhibit rupture of a wire used for slicing an ingot.
2. Brief Description of the Prior Art
After top and tail parts are cut off an ingot produced by a pulling method or the like, the ingot is ground at its periphery, subjected to orientation flat processing and then sliced to wafers of predetermined thickness. Although an inner blade slicer has been used so far for such ingot-slicing, it can not well cope with enlarged of wafers. Therefore, a wire saw using a piano wire has been widely adopted in response to an intensified demand for wafers enlarged in size.
A conventional wire-sawing machine has three grooved rollers 1-3, one of which (the roller 3) is coupled to a drive motor 4, as shown in FIG. 1. A wire 5 is pulled out from a reel 6, passed around the grooved rollers 1 to 3 multiple times and then wound on another reel 7. A tensioner 8 applies a tension to the wire 5. Thus, the wire travels in a stretched state along a travel path around the grooved rollers 1 to 3.
An ingot 9 to be sliced is fixed to a holder 10 using a proper adhesion jig and located at a position between the grooved rollers 1 and 2. The ingot 9 is sliced to a plurality of wafers by cutting motion of the wire 5. During slicing, slurry 11 is supplied from a slurry tank 12 through a supply tube 13 to a nozzle 14, sprayed onto the wire 5, collected in a pan 15 and then returned to the slurry tank 12, in order to promote the cutting motion. The slurry 11 is cooled by circulation between the slurry tank 12 and a heat exchanger 16.
The wire 5 is sent out form the reel 6 through deflector rollers 18 to the grooved rollers 1 to 3, used for slicing the ingot 9 during one way passing along a direction d.sub.1, forwarded through other deflector rollers 18 to another reel 7, and then wound on the reel 7, as shown in FIG. 2. The wire 5 may be bi-directionally forwarded, instead. That is, a travel of the wire 5 along a direction d.sub.2 together with the travel along the direction d.sub.1 is periodically repeated in the manner such that the wire 5 is successively wound on the reel 7 as a whole.
A tension is applied to the wire 5 in order to slice the ingot 9 under stable conditions. Such a tension is applied by the pendulum-type tensioner 8 (shown in FIG. 1), a balance weight 17 (shown in FIG. 2) or a powder clutch (not shown). For instance, the wire 5 is sent along a travel path around a dancer roller 19 provided between the inlet-side deflector roller 18 and the outlet-side deflector roller 18. The dancer roller 19 supports a balance weight 17 for application of a predetermined tension.
The tension applied to the wire occasionally increases during travelling of the wire 5. Especially, increase of tension likely occurs when a travelling direction of the wire 5 is switched as d.sub.1.fwdarw.d.sub.2 or d.sub.2.fwdarw.d.sub.1. An increasing part of the tension is somewhat absorbed by upward turning of the tensioner (FIG. 1), upward motion of the dancer roller 19 (FIG. 2) or rotation of a powder clutch (not shown). However, abrupt increase of the tension is not compensated for with such motion of the tensioner 8, the dancer roller 19 or the powder clutches.
Such abrupt increase of the tension, i.e. abnormal tension, causes rupture of the wire 5 regardless of such tension-controlling means as the tensioner 8, the dancer roller 19 or the powder clutch. When the wire 5 is broken, wire-sawing operation is inevitably interrupted. In addition, a lot of works and time are required for detaching the broken wire 5 and stretching a new wire 5, resulting in reduction of productivity.